Petrol stalling problem

[VEEMAN]

I currently have the following problem with my MK6 2.3L petrol / LPG on a 2004 plate.
When firing up from cold the engine fires up no problem and idles at about 1200rpm ( due to choke ). The problem ( running on petrol ), is if the engine is slightly revved up the engine will return back to 1000rpm and keep dropping past this until the engine stalls. The engine will fire up again no problem and idle, as long as the engine is not revved.
When the engine is warm, none of the above problems happen, and the revs return back to idle at 950rpm approx. after the engine has been revved.
I have no fault codes on the ECU. I have changed the idle air pass valve, water coolant temp sensor, MAS all with new components. All the vacuum pipes seem in order with no splits, not crushed or collapsed etc. Also reset the ECU with disconnecting the battery and ran for 300 miles, still the same problem.
Has anybody came across this situation before and can point me where to look. I do not want to start changing components for the sake of it , and end up with the same fault.
Any advice welcome.
Cheers
Veeman

[Altransit]

I'm not familiar with the engine fitted to your Mk6, but on the older Pinto EFi engine, this could be caused by a fault with the throttle body, it could be as simple as needing a good clean

[mealic]

Make sure that the electricval connections plug is connected firmly on the MAF sensor. Change the Lambda sensor (located on the right of the engine in the exhaust downpipe) a universal available on the bay for about £25.

[VEEMAN]

Thanks for the replies. First of all the engine is a ESFC 2.3 l petrol.
I have already cleaned the throttle body, and already renewed the throttle position sensor. Both Lambda probes have been renewed about 6 months ago. Van still came up with the same problem. Had a mobile diagnostic bloke check the van out and he told me that the Lambda sensors where working correct, neither came up with a fault code. He could not find any fault codes at all.
Keep the suggestions coming please. I have talked to 2 mechanics and they both suggested what work I had already done. They where both stumped as well for a solution to this fault.
Can I back probe the MAF sensor plug ? if so what readings do you expect to get on what pins?
Cheers
Veeman

[mealic]

I had a similar problem on mine a little while ago. Fitted a replacement sensor so went along the route of "oh well thats been changed,lets look for something else" and it turned out that the new sensor was faulty too!!

How much fuel is in the tank. Can you drain it and maybe put some higher octane in, with perhaps a petrol injection Millers cleaner .

[VEEMAN]

Thanks once more for the reply.
I know what you are saying about a bad sensor. That happened on the throttle position sensor I put in to replace the old one. I tested it on ohms and found the sweep was all over the place on ohms. Replaced it with another and it was fine.
As to fuel level, at the moment is quarter of a tank. Could drain it and put some injector cleaner in it with fresh fuel. But I do not think it is a fuel starvation or blockage as it runs fine in about a mile after starting from cold.
Had one thought, to test the Map sensor and see if that is within specs. This could give me rough idling as well. Will try it tomorrow as it is the only sensor I have not looked at. It does have a bearing on the injector opening time as well as mixture. It's worth a shot to eliminate.
Once more thanks for the advice.
Cheers
Veeman

[rogerw]

Which temp sensor did you replace, there are two? From what you say seems like 'choke' isnt working. Underfuelling what ever causes that ?

[VEEMAN]

I have changed the right sensor. I know there are two, one for the water temperature and the second is for the cooling fans.
Had a look at the MAP sensor today. On the output of the sensor there was a voltage of 4.8v on ignition on only. Starting the van up it dropped to 1.09v floating 0.02v. When the engine was revved up the voltage dropped to 0,30v up to 0.75v. The engine then stalls when the voltage was about 0.40v.
So should this MAP sensor voltage drop below 1.09v when the engine is revved. Does anyone know?
Keep the suggestions coming all info is helpful in solving this problem.
Cheers
Veeman

[mealic]

I presume that you are talking about the MAF (mass air flow) sensor. From the airbox to the throttle body. Check to make sure there are no air leaks. You can clean this carefully using contact cleaner.
I cannot make a comparison as I have removed the stock airbox and have an induction kit and filter attached straight to the throttle body via the MAF.

How does it run on LPG?

[VEEMAN]

Not looking at the MAF sensor at all. The readings above are readings I took from the MAP sensor, located on the top o/s above the air filter. Looking again at the readings I got, it's indicating to me that when the revs increase the signal is getting sent to the ecu that it is lean. Hence this is why the engine is stalling when cold.
What I would expect, when the engine is revved the signal from the sensor should increase towards the 4.8v level not go below 0.7v.
Any one shed some light on the readings.
By the way it runs and switches fine on LPG no problems, as on petrol when the engine is at running temperature. This stalling only happens when the engine is cold, once warm no problems.
Any more advice.
Cheers
Veeman

[rogerw]

You MAP is responding. I can take some voltage readings from my van, for you, but not sure exactely whereto probe,. Other than near air filter box, so need a pic of MAP really

[VEEMAN]

Thanks for your help with a few readings.
The map sensor is above the air filter, which is the left as you look at the front of the van. If you follow the bonnet hinge towards the wing you will see attached a bracket with a black plastic box with a small vacuum hose attached. There is a plug also attached to the black box ( MAP sensor ). This plug has three wires going into the plug. Back probe the centre wire of the plug ( +ve lead of multimeter ) and -ve lead to earth.
With the ignition turned on only it should read near to 5V. Start the engine up and you should see this value drop to 0.8V - 1.22V at idle. Rev the van up and see what values you get ( mine sometimes drops below 0.3V when engine comes back to idle. Note all my tests have be done with a cold engine.
Hope you can understand the above. Interesting to see your results.
Cheers
Veeman

[rogerw]

Surprised there is any room above filter box, but will have a look when its daylight.

[rogerw]

No box MAP. I have a disc shaped sensor with two pipes leading off.

[rikki19]

Thanks for your help with a few readings.
The map sensor is above the air filter, which is the left as you look at the front of the van. If you follow the bonnet hinge towards the wing you will see attached a bracket with a black plastic box with a small vacuum hose attached. There is a plug also attached to the black box ( MAP sensor ). This plug has three wires going into the plug. Back probe the centre wire of the plug ( +ve lead of multimeter ) and -ve lead to earth.
With the ignition turned on only it should read near to 5V. Start the engine up and you should see this value drop to 0.8V - 1.22V at idle. Rev the van up and see what values you get ( mine sometimes drops below 0.3V when engine comes back to idle. Note all my tests have be done with a cold engine.
Hope you can understand the above. Interesting to see your results.
Cheers
Veeman

I don't have this map sensor on a 2001 petrol only .... does it apply only to lpg equiped vans ?